This invention relates to a process for preparing a colloidal solution of antimony pentoxide. More particularly, it relates to a novel process for preparing a colloidal solution of antimony pentoxide by obtaining an antimony pentoxide gel from sodium antimonate and an inorganic acid, and then peptizing the gel by use of a base.
The colloidal solution of antimony pentoxide (hereinafter referred to as "antimony pentoxide sol") is used as a flame retardant or the like for plastics, fibers, etc. Conventional processes for preparing the antimony pentoxide sol are roughly classified into an ion exchange method and a hydrogen peroxide method. As the former ion exchange method, there may be mentioned a method in which potassium antimonate is deionized (U.S. Pat. No. 3,860,523), or a method in which sodium antimonate is deionized (U.S. Pat. No. 4,110,247). The antimony pentoxide sols obtainable by this method have good dispersibility as they are comprised of particles almost spherical shape, and are characteristic in that they can further be made in high concentration. However, it is difficult according to this ion exchange method to effect ion exchange when the concentration of antimony pentoxide exceeds 10%. Moreover, this method has a drawback in that it requires complicated operations such that subsequent operations for separation and regeneration of ion exchange resins must be carried out. The latter hydrogen peroxide method is a method in which antimony trioxide is oxidized by use of hydrogen peroxide at a high temperature (see, U.S. Pat. No. 4,022,710; Japanese Unexamined Patent Publication No. 21298/1977; U.S. Pat. Nos. 4,028,226 and 4,026,819). This method shows high productivity because it is possible to obtain antimony pentoxide sols comprising about 30% antimony pentoxide directly, but inadvantageous in that the viscosity icreases when antimony pentoxide exceeds 30%. Moreover, this method has drawbacks that colloidal particles of the sols are irregular in shape so that there is obtained only poor dispersibility and, because of strong surface activity, poor compatibility with resin emulsions and the like.